Environmental magnetism and its application towards palaeomonsoon reconstruction

Abstract

Environmental mineral magnetic techniques are designed to measure the response of natural materials to a range of artificially applied magnetic fields. Magnetic measurements are easily and rapidly made in the laboratory or in situ, and they are highly accurate apart from being non-destructive. The magnetic properties of samples can be used to carry out sediment provenance studies, understand magnetic grain-size, attempt palaeoclimatic reconstruction, and monitor anthropogenically-generated particulate atmospheric pollution. Mineral magnetic measurements have been performed by the Environmental Magnetism Group (IIG) on samples collected from India covering different depositional environments and provenance, namely the Himalayan lake deposits of Garbayang and Goting (-10 ka to 30 ka), modern playas within the Thar desert (-10 ka), Nalsarovar (-6 ka), Lonar (-50 ka) and Mastani (-5 ka), and near shore deltaic and estuarine environments of Godavari, Iskapalli and Mandovi. Apart from these studies, the technique has also been applied to Himalayan loess deposits and late Quaternary palaeosols of Saurashtra. Case studies from these diverse environmental situations reveal the utility and application of mineral magnetic techniques in palaeomonsoonal reconstruction. Specifically, these studies bring to the fore the sensitivity of the S-ratio (backfield IRM/SIRM) to climatic changes, as opposed to magnetic susceptibility (x). Our studies caution against using x indiscriminately in palaeomonsoon reconstruction. Efforts are underway to build-up a master curve of secular variation for the Indian subcontinent and will serve as a relative chronological tool for the Holocene.